Indirectly heated cathode



June 4, 1963 H. F. DICKSON, JR., ETAL 3,092,743

INDIRECTLY HEATED CATHODE Filed March 11. 1960 INVENTORS Herberf F D/c/fso/Z Jz' PdU/ Haas United States Patent 3,092,748 INDIRECTLY HEATED CATHODE Herbert F. Dickson, In, and Paul Haas, Seneca Fails, N.Y., assignors to Sylvania Electric Products Inc, a corporation of Delaware Filed Mar. 11, 1960, Ser. No. 14,470 6 Claims. (Cl. 313-270) This invention relates to electron discharge devices and more particularly to electrode assemblies for these devices.

In an electron discharge device such as a cathode ray tube, the thermionic cathode cylinder normally is indirectly heated by a length of coiled insulated resistance wire disposed within the cylinder. The cathode is rigidly headed to a ceramic support disc, which is in turn disposed within the first grid of the tube. An .assembly of this type requires an undesirable amount of power to operate since the efficiency of heat transfer to the cathode cylinder from the resistance Wire is relatively low. Also, the mass of the cylinder and ceramic support causes a large amount of conduction and radiation losses from the entire assembly.

Accordingly, it is an object of this invention to reduce the power required to adequately operate an indirectly heated cathode assembly for an electron discharge device.

A further object is to provide an assembly for such a device which is compact, has high thermal utilization efliciency as a unit, and is adapted for easy assembly and alignment with other electrodes of the device.

The foregoing objects are achieved in one aspect of the invention by the provision of an indirectly heated cathode assembly adapted for use in an electron discharge device which utilizes a heater embedded cathode structure suspended across an opening provided in an insulating disc by lead wire connections with the ends of the heater and the cathode tab. Heat conduction and radiation losses from the assembly are controlled.

For a better understanding of the invention, reference is made to the following description take in conjunction with the accompanying drawings in which:

FIG. 1 is a plan view of a typical cathode ray tube which is adapted for utilization of the invention;

FIG. 2 is a top view of the cathode assembly;

FIG. 3 is a sectional view taken along line 33 of FIG. 2 showing the manner in which the cathode is supported by lead wires;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2 showing the relationship of a lead and a groove in the support formed in a preferred manner; and

FIG. 5 illustrates the cathode assembly mounted within the first grid of a tube which may be of the type shown in FIG. 1.

Referring to FIG. 1, .a cathode ray tube 11 illustrates one type of electron discharge device which may advantageously utilize the invention. Tube 11 comprises an envelope 13 having a face plate 15 with a fluorescent screen 17 formed on the inner surface thereof. A cathode ray tube gun 19 formed to provide the source, modulation and acceleration of electron beam 21 is disposed within neck 23. The beam is conventionally deflected by coils 25 to scan the high potential operated screen 17.

Electron gun 19 may comprise a plurality of electrodes including a cathode assembly 27 and a first grid 29. The cathode assembly is constructed to operate with minimum power, which makes tube 11 uniquely adapted for portable and transistorized electrical equipment use. This low power feature is accomplished by employing a cathode 31 having a given configuration with a heater 33 embedded or enclosed therein to provide maximum heat transfer efliciency and utilization coupled with a cathode and heater mounting adapted to minimize heat conduction and radiation losses.

3,092,748 Patented June 4, 1963 A heater embedded cathode pellet 31 of the type shown and described in co-pending application Ser. No. 14,472, entitled Heater-Cathode Assemblies, filed concurrently herewith by the common assignee, has been found to have excellent low power characteristics. The spiral reverse coiled insulated wire of heater 33 may be packed within nickel pellet 31 by powder metallurgy techniques. Such a cathode pellet may have a diameter of .050 inch, a thickness of .011 inch, and a heat radiating surface of .0054 sq. inch, which is a 25:1 reduction over the conventional indirectly heated cathode sleeve radiating surface of about .136 sq. inch normally used in tube 11. It can be seen, therefore, that the heater configuration and the embedded association of the heater in the cathode plus the minimum heat radiating surface allows maximum utilization of the heater power. Of course, any highly thermal eflicient heaterenclosed cathode assembly could conceivably be used, but the illustrated cathode pellet 31 is preferred.

Since cathode 31 and heater 33 are physically mounted and electrically energized under normal operating circumstances, means for accomplishing the mounting and electrical connections are provided which minimize and control heat losses so that the advantages of the high thermal etficiency cathode are fully utilized. Essentially, this is done by suspending cathode 31 across an opening 35 provided in ceramic support disc 37 and providing a unique mounting therefor. The cathode is positioned by means of electrical connections between the uncoated ends 39 of heater 33 and heater leads 41, and between cathode connector or tab 43 and cathode lead 45. Such an arrangement provides the necessary connections and mounting support while minimizing and controlling heat radiating surface areas and conduction paths. In this regard, it has been found that the ratio of cathode embedded length to free length of heater wire 33, as well as the ratio of coated to uncoated free length of Wire 33 are important factors to consider. Of course, the total length and radiating surface of tab 43 is also a factor.

Referring to FIGS. 2 and 3, it can be seen that insulating coating 47 covers the entire central embedded portion but only part of the free ends of heater 33. With a cathode pellet 31 of the size described above and adapted for operation at .20 watt and 1.5 volts, the heater wire is preferably made of about .625 inch of .001 inch diam eter tungsten Wire, spiral reverse coil wound, and cataphoretically coated with aluminum oxide to provide l3. coated d ameter of .003 inch. The ratio of the central embedded wire length to non-embedded or free leg length of heater 33 is maintained greater than unity but not greater than 4:1, and preferably between 2 to 1 and 2.5 to 1 while the total length of coated portion 47 outside of pellet 31 does not exceed .75 times the total free leg length of heater 33. The cathode tab 43 may be a nickel alloy .006 inch wide, .002 inch thick and at least .050 inch long. If the tab length becomes too small, the conduction losses. increase undesirably.

In order to provide a rugged and accurate mounting for cathode 31, radially spaced leads 41 and lead connector 45 pass through spaced apertures 49 in disc support 37, and are bent to lie along the upper face of the disc. Lead wires 41 extend partially across central opening 35 and are welded to ends 39 of the heater as illustrated at points 51. It is preferable to flatten wires 41 at their extremities to aid in the production of a good weld and to laterally stabilize the wires within radial V- shaped grooves 53, FIG. 4. Cathode lead Wire connector 45, which also lies within a groove 53, is bent downwardly to pass within opening 35. The end of the C011.

cement 55 are used to rigidly afiix leads 41 and connector 45 in position upon support disc 37. Preferably, the cement is used on the top and bottom surfaces of disc 37 around the leads and connector adjacent the entrance of apertures 49 as well as across connector 45 at a position along groove 53. 7 It is contemplated that leads 41 and 45 may be mounted in some other manner such as by passing through some type of apertures formed in disc 37 to extend from the apertures laterally into opening 35.

When using a heater-cathode pellet 31 of the size and power rating enumerated above, it would be preferable to use a steatite disc 37 of about .355 inch in diameter and .062 inch thick. Central opening 35 may be .170 inch in diameter and the spaced longitudinal apertures 49 disposed intermediate the central opening and the periphery of disc 37 may have a .020 inch diameter. It has been found that apertures 4? are satisfactorily located at a radius of .265 inch from the center of the disc. Leads 41 and 45, which are preferably made of molybdenum, may have a diameter of about .015 inch.

During the mounting operation wherein pellet 31 is attached to disc 37, the pellet is rotatively aligned so that the heater wire ends 39 and tab 43 contact their respective leads 41 and connector 45 without distortion. Pellet 31 may be held at an appropriate distance above the top of disc 37 and spaced centrally within opening 35 by any convenient means such as an appropriate jig. Welding of the leads and wires provides the mounting for the assembly as recited above. It has been found that one of the more important aspects of this mounting procedure is to assure handling of the parts so that there will be no distortion of the heater wire and tab, which is an essential condition for maintaining the upper surface of pellet 31 in 'a parallel relationship with the upper surface of disc 37. Of course, the importance of this relationship is based upon the premise of using the preferred illustrated type of cathode-grid 29 mounting arrangement. Variations in longitudinal positioning of these surfaces can be compensated for to some extent in the actual assembly of the cathode pellet and disc relative to grid 29.

Referring to FIG. 5, assembly 27 may be mounted upon a metallic retainer 57 provided with a flange 59 overlying and circumscribing shoulder 61 of disc 37. Assembly 27 is held rigidly to metallic retainer 57 by means of insert 63, which abuts the bottom of disc 37 opposite shoulder 61. The insert and retainer may be welded or otherwise attached to one another. During fabrication of a cathode assembly, it has been found preferable although not necessary, to apply cathode emissive material 65 to the upper surface of pellet 31 after assembly 27 has been attached to the retainer and insert since minimum handling is thereafter required. Cathode material 65 may be of the conventional triple carbonate type.

When the low heater power cathode assembly 27 is to be used with the cathode ray tube 11 such as shown a generally in FIG. 1, it is mounted within the cylindrical 'first grid 29 of gun 19. The aperture 67 in end wall 69 of the grid is aligned with surface of cathode material 65 and spaced therefrom in accordance with the requirements dictated by the desired electrical characteristics of the tube. This cathode to grid spacing may be accurately achieved by any convenient means such as an air or optical comparator or a capacitance gauge (not shown). After the proper spacing is achieved, grid 29 is then welded to retainer 57. The complete cathode grid assembly, FIG. 5, may then be mounted with the other elements of gun 19 in the conventional manner. Of course, it is contemplated that retainer 57 and insert 63 may be formed as an integral unit having the general mounting faculties of the illustrated parts.

The cathode assembly shown and described herein provides a unique and dependable low-power consumption unit not heretofore realized for'ope-ration in indirectly heated cathode type electron tubes. This assembly facilitates the fabrication of tube components which lead the trend toward full utilization of transistorized, portable, and other low power equipment. It is notable that although the invention provides percent saving in power for the specific assembly illustrated over conventional structures, the cathode emission and life characteristics are equal and in some respects superior to the conventional cathode assemblies. The specific dimensions and characteristics for the components were given above as an example to illustrate an assembly adapted for use in any otherwise standard construction current television picture tube which normally uses a. common but. arbitrarily selected 1.125 inch diameter neck. It was found that a tube employing the invention works well not only with a constant voltage source, but with a variation over the useful Working range of dry cells, namely 1.2 to 1.55 volts. Also, although the contemplated cathode operating temperature for the specific structure illustrated is 775 degrees C., variations of from 650 degrees C. to 800 degrees C. over a range of from 1.2 to 1.6 volts does not abnormally afiect operation. Heater cycling tests at overrated voltage conditions indicated that there is no unusual problem with heater burn-out failures.

The type of electron tube with which assembly 27 will be utilized will determine in part many of the parameters and configurations-of the elements. However, the invention contemplates any such device using the heat utilization and controlled heat loss principles involved herein.

. Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein Without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An indirectly heated cathode assembly adapted for use in an electron discharge device comprising an insulating support provided with a central longitudinal opening, radially spaced leads mounted upon said support extending partially across said central opening, and an indirectly heated cathode structure employing a metallic cathode base having a connector attached thereto and a heater partially enclosed'therein with the free ends thereof extending outwardly from said base, a separate one of said leads being connected to each of said heater free ends and to said cathode connector to provide electrical contacts with said heater and cathode base and to suspend the structure across said central opening.

2. An indirectly heated cathode assembly adapted for use in an electron discharge device comprising an insulating support provided with a central longitudinal opening, radially spaced leads attached to said support extending partially across said central opening, and an indirectly heated cathode structure employing a metallic cathode base pellet, a tab connected to said pellet, and

a heater having a given central length thereof embedded in said pellet and outside legs thereof extending from said pellet, said given embedded length ranging from 1 to 4 times the total outside leg lengths, the embedded length of said heater and not more than .75 times said total outside leg length being covered with an insulating coating, a separate one of said leads being connected to each of the opposite ends of said heater legs and tothe tab to provide electrical connections for said heater and cathode base pellet and to suspend the structure across said support central opening. T

3. An indirectly heated cathode assembly adapted for use in an electron discharge device comprising a ceramic disc provided with a central longitudinal opening, spaced longitudinal apertures disposed intermediate the peripha lead wire passing through said apertures formed to provide an end thereof lying within said grooves and partially extending across said central opening, and an indirectly heated cathode structure employing a metallic cathode base, a tab connected to said base, and a heater having the central portion thereof enclosed within said base and the outside legs thereof extending from said base, a separate one of said lead wires being connected to each of the opposite ends of said heater legs and to the tab to provide electrical connections for said heater and cathode base and to suspend said structure across said disc central opening.

4. An indirectly heated cathode assembly adapted for use in an electron discharge device comprising a ceramic disc provided with a central longitudinal opening, three spaced longitudinal apertures disposed intermediate the periphery of said disc and said central opening, and spaced radial grooves formed in one face of said disc interconnecting the central opening with each of said spaced apertures, a lead wire passing through each of said apertures formed to provide an end thereof lying within said grooves and partially extending across said central opening, and an indirectly heated cathode structure employing a metallic cathode base pellet, a tab connected to said pellet, and a heater having a given central length thereof embedded in said pellet and outside legs thereof extending from said pellet, said given embedded length ranging firom l to 4 times the total outside leg lengths, the embedded length of said heater and not more than .75 times said total outside leg length being covered with an insulating coating, the ends of two of said lead wires being connected to the opposite ends of said heater legs with the tab being connected to the end of the third lead wire to provide electrical connections for said heater and cathode base pellet and to suspend said structure across said disc central opening.

5. In an electron discharge device, an indirectly heated cathode assembly comprising an insulating disc provided with a central longitudinal opening, radially spaced lead wires lying along one face of said disc extending partially across said central opening, an indirectly heated cathode structure employing a metallic cathode base having electron emissive material deposited thereon, a tab attached thereto and a heater partially enclosed therein with the free ends thereof extending outwardiy from said base, a separate one of said Wires being connected to each of the ends of said heater and to said tab to provide electrical connections for said heater and cathode base and to suspend said structure across said disc central opening; a cylindrical grid surrounding said assembly having an end Wall formed with an aperture therein aligned relative to said cathode base; and means telescoped Within and affixed to said grid formed to rigidly support said disc to space position said cathode base relative to the grid end wall.

6. In an electron discharge device, an indirectly heated cathode assembly comprising an insulating disc provided with a central longitudinal opening, radially spaced lead Wires lying along one face of said disc extending partially across said central opening, an indirectly heated cathode structure employing a metallic cathode base having electron emissive material deposited thereon, a tab attached thereto and a heater partially enclosed therein with the free ends thereof extending outwardly from said base, a separate one of said wires being connected to each of the ends of said heater and to said tab to provide electrical connections for said heater and cathode base and to suspend said structure across said disc central opening; a cylindrical grid surrounding said assembly having an end Wall formed with an aperture therein aligned relative to said cathode base; a retainer telescoped within and affixed to said grid formed to provide a rim overlying said disc shoulder to space position said cathode base relative to the grid end Wall; and an insert positioned within said grid abutting the face of said disc opposite to the shoulder thereof to rigidly affix said assembly between the rim and said insert.

References Cited in the file of this patent UNITED STATES PATENTS 2,335,818 Turnbull Nov. 30, 1943 2,413,689 Clark Ian. 7, 1947 2,888,591 Schmidt May 26, 1959 2,906,901 Wilde Sept. 29, 1959 

1. AN INDIRECTLY HEATED CATHODE ASSEMBLY ADAPTED FOR USE IN AN ELECTRON DISCHARGE DEVICE COMPRISING AN INSULATING SUPPORT PROVIDED WITH A CENTRAL LONGITUDINAL OPENING, RADIALLY SPACED LEADS MOUNTED UPON SAID SUPPORT EXTENDING PARTIALLY ACROSS SAID CENTRAL OPENING, AND AN INDIRECTLY HEATED CATHODE STRUCTURE EMPLOYING A METALLIC CATHODE BASE HAVING A CONNECTOR ATTACHED THERETO AND A HEATER PARTIALLY ENCLOSED THEREIN WITH THE FREE ENDS THEREOF EXTENDING OUTWARDLY FROM SAID BASE, A SEPARATE ONE OF SAID LEADS BEING CONNECTED TO EACH OF SAID HEATER FREE ENDS AND TO SAID CATHODE CONNECTOR TO PROVIDE ELECTRICAL CONTACTS WITH SAID HEATER AND CATHODE BASE AND TO SUSPEND THE STRUCTURE ACROSS SAID CENTRAL OPENING. 